DuraVent 3" PelletVent Pro Storm Collar - 3PVP-SC Laser-welded, double-wall pipe with a .012" inner wall of 444 Stainless steel Outer wall of .018" laser welded Galvalume Encapsulated O-ring gives secondary seal to system. 1" clearance to combustibles in the US and Canada. Storm collar, used in combination with the roof flashing to make weathertight.